The literature discloses the production of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (referred to in the inventive specification as DOPO) and a number of its derivatives. For example, SAITO describes, in DOS 20 34 887, the production of DOPO and various DOPO derivatives. DE 26 46 218 deals with the reaction of DOPO with itaconic acid and itaconic anhydride, and further modifications of these adducts. ENDO et al. establish in this connection that adducts of DOPO with maleic acid and maleic anhydride, and esters which can be produced therefrom are unsuitable for copolymerizations due to an inadequate degree of esterification of the carboxyl groups of the adducts. DIETRICH et al. also restrict themselves, in DE 195 22 876, to the production of, inter alia, DOPO and DOPO derivatives and reaction products thereof with itaconic acid or itaconic acid compounds, and the use thereof for flameproofing polyester fibers. DOPO derivatives which are obtained specifically by reaction with epichlorohydrin are described by UTZ and SPRENGER in EP 0 806 429. These products are intended to be used for incorporation in epoxy resins. The flameproofing of epoxy resins is also the theme of the paper by LIN, WU and WANG (J. APPL. Polym. Sci. 78, 2000, pp. 228-235). To produce the epoxy resins, they use DOPO adducts with maleic acid and with itaconic acid and react these with diglycidyl or bisphenol A. In EP 1 090 922, TAKEUCHI et al. deal with the production of DOPO from o-phenyl-phenol and of DOPO derivatives with α,β-unsaturated carboxylic acids, and the esters, diols etc. thereof, which are always used together with compounds of divalent metals, preferably zinc, for incorporation in polyesters. This is said to suppress the oxidation of the antimony catalysts during the production of flameproofed polyesters.
It is common to all of these specified methods for producing DOPO derivatives that they use exclusively olefinically unsaturated compounds as reactants during the formation of adducts of DOPO. The number of DOPO molecules which can be added per double bond and thus generally per olefin molecule is therefore limited to one. Exceptions would be dienes or polyenes with correspondingly longer carbon chains, but these are not known from any of the protected rights or literature references. This gives rise to the disadvantage that the phosphorus content of these organic phosphorus compounds has an upper limit, meaning that a relatively high minimum amount of flame retardant as comonomer is required in order to achieve a certain flame retardancy effect on incorporating these flame retardants into polymers. This in turn results in an unfavorable effect on the properties of the copolymers formed.